Inspection device for crystal defect of silicon wafer and method for detecting crystal defect of the same

ABSTRACT

An inspection object silicon wafer for the purpose of detecting crystal defects and the method of detection thereof, which make easy the detection of the number and location of the defects formed on the surface of the silicon wafer by performing heat treatment and epitaxial growth under a temperature condition in which the natural oxide film is removed but the state of the surface of the silicon wafer is preserved, specifically under a hydrogen atmosphere of normal pressure and a temperature between 900° C. and 1080° C., through which defects having pits and projections are generated on the surface of the epitaxial layer, and by detecting the defects having pits and protrusions by a light scattering type particle inspection apparatus.

FIELD OF THE INVENTION

The present invention relates to a silicon wafer for the purpose ofdetecting crystal defects and the method of detection thereof,specifically to a silicon wafer for the purpose of detecting crystaldefects and the method of detection thereof, in which crystal defectsformed on the surface of the silicon wafer are shown up in pits andprojections by forming epitaxial layer.

TECHNICAL BACKGROUND

A silicon wafer is the general term for a silicon single crystalsubtrate (hereafter may be referred to as “mirror surface wafer”) madeby slicing the single crystal grown by Czochralski method (CZ method) orFloating zone melting method (FZ method) to thin plate and furtherpolishing the surface to a mirror surface state (hereafter may bereferred to as “mirror surface wafer”) or a silicon epitaxial waferobtained by forming a thin film of silicon single crystal on the mirrorsurface wafer by vapor phase growth. A variety of crystal defects suchas point defect, line defect, plane defect, etc. are formed in a siliconwafer. Among these, the one appearing on the surface (hereafter may bereferred to as “surface defect”) exerts an influence to the electriccharacteristic of semiconductor devices having circuits formed in nearproximity to the surface of the silicon wafer, and the adequate controlof the condition of detect generation is needed.

As the surface detect has ordinarily no virtual pit or projection, it isshown up in pit or projection by preferential etching to be detected.Sirtl solution, Secco solution, and Wright solution are well known assolutions for preferential etching. For example, Secco solution is aaqueous solution of 28.86 mol of 50% hydrofluoric acid and 0.15 mol ofpotassium bichromate (K₂Cr₂O₇). These are etching solutions whichoxidize silicon with the oxidizing agent and solve the oxide film withhydrofluoric acid. Crystal defects are made apparent by producing pitsand/or projections through a phenomenon that the speed of oxidation bythe oxidizing agent differs between oxidation of perfect crystal andthat of a region where crystal defects or stresses exist.

Surface defects made apparent by the preferential etching are observedby a normalski type differential interference microscope to determineits density. The normalski type differential interference microscopegives a three-dimensional appearance of irregularity and ruggedness ofheight of 3.5 nm or higher, and the inclination of plane is observed asa difference in interference color.

The density of surface defects is determined by observing 5 to 9 pointsof area or scanning in the direction of diameter by 100× to 400×magnification. The number of defects per silicon wafer is worked outfrom the detected number of defects and the measurement area.

For example, when a silicon wafer of 200 mm diameter is scanned in thedirection of diameter in the shape of a cross by the differentialinterference microscope, if the diameter of the field of view of themicroscope is 1.7 mm, then the measurement area is:

1.7 mm×200 mm×2=680 mm².

Supposing that one surface defect is observed by the scanning, thenumber of surface defects per silicon wafer is:

1(defect)×(π×100² mm²)÷680 mm²46(defect).

The above value 46 of the number of surface defects per silicon wafer iseffective only when the surface defects are distributed evenly. When thesurface defects appear localized in a region, the above value differsfar from the real state. Also, when the density of surface defects issmall, for example, when the number of surface defects per silicon waferof diameter of 200 mm is under 46, there is high probability that nosurface defect exists in the region scanned by the microscope anddetection is substantially impossible.

Further, in the case of a silicon wafer of resistivity of 0.02 Ωcm orsmaller, surface defects are difficult to appear by etching withaforesaid preferential etching solutuon.

On the other hand, there is visual inspection using collimated light asa method of simply inspecting the whole surface of a silicon wafer.

In the visual inspection, when the surface of a preferentially-etchedsilicon wafer is irradicated by collimated light, scattered light isreflected from surface defects. The distribution pattern of the surfacedefects is observed by viewing the scattered light in a darkroom. But,by this visual inspection, mapping of the surface defects on the wholesurface can not be obtained by using a machine, and the accuratedetermination of the number and location of surface defects is notpossible.

Also, when trying to detect the surface defects appearing on the surfaceof the silicon wafer by preferential etching by means of the lightscattering type particle inspection apparatus, the etched figuresgenerated by the preferential etching are detected similarly asparticles together with the surface defects, and the surface defects cannot be discriminated from the etched figures.

SUMMARY OF THE INVENTION

The present invention was made to solve the aforementioned problem.Accordingly, the object of the invention is to provide a silicon waferon the surface of which the number and location of crystal defectsgenerated can be easily detected and the method of detection thereof.

Usually, before performing epitaxial growth, heat treatment is performedin a hydrogen atmosphere at normal pressure and a temperature between1100° C. and 1200° C. for etching the natural oxide film formed on thesurface of a silicon wafer and for etching the silicon surface for thepurpose of eliminating the crystal defects generated on the surface ofthe silicon wafer. The etching of the natural oxide film and that of thesilicon surface are instantly completed at the above-mentionedtemperature range. Then, by vapor phase growth of silicon single crystalthin film on the surface of the cleaned silicon wafer, an epitaxiallayer with largely reduced surface defects is formed.

The etching of the natural oxide film by hydrogen can be effected attemperatures above 900° C. at normal pressure, but, on the other hand,the speed of etching a silicon surface by hydrogen decreases rapidlywhen the temperature of heat treatment is lower than 1100° C. and theetching hardly occurs below 1080° C.

Therefore, if a silicon wafer is heat-treated at a temperature between900° C. and 1080° C. in a hydrogen atmosphere of normal pressure, thenatural oxide film is completely removed but the surface of the siliconwafer is hardly etched, thus the surface condition is preserved and alsothe surface defects are preserved without being removed.

After this heat treatment, if a silicon single crystal film is grown invapor phase on the silicon wafer at a temperature between 900° C. and1080° C. at normal pressure, the surface defects are preserved duringthe vapor phase growth and transferred to the epitaxial layer. Thus, thesurface defects on the silicon wafer become apparent on the surface ofthe epitaxial layer as crystal defects having pits and/or projections.

As the crystal defects appearing on the surface of the epitaxial layerhave pits and/or projections, they are detected by a light scatteringtype particle inspection apparatus like particles are detected.

The present invention was made based on the above mentioned findings.The inspection object silicon wafer for the purpose of detecting crystaldefects is characterized in that epitaxial growth is made on the surfaceof a mirror surface wafer which the natural oxide film is removed ofwithout surface defects being eliminated to make the crystal defectshaving pits and/or projections appear on the surface of the epitaxiallayer.

The inspection object silicon wafer for the purpose of detecting crystaldefects is manufactured through a process of heat treatment in which thenatural oxide film is removed without the surface defects of a mirrorsurface wafer being eliminated, and a process of epitaxial growth inwhich the epitaxial growth is made on the surface of the mirror surfacewafer and the crystal defects having pits and/or projection aregenerated on the surface of the epitaxial layer.

More concretely, the heat treatment process and epitaxial growth processare preferably performed under a hydrogen atmosphere of normal pressureat a temperature between 900° C. and 1080° C.

The crystal defect detection method according to the present inventionrelates to a detection method which can easily detect the number andlocation of the crystal defects formed on the surface of a silicon waferby use of said inspection object. The method is characterized in that;by making epitaxial growth on the surface of a silicon waferheat-treated under a temperature condition in which the natural oxidefilm is removed but the surface state of the silicon wafer is preserved,crystal defects having pits and projections are made to appear on thesurface of the epitaxial layer; and the crystal defects having pits andprojections are detected by a light scattering particle inspectionapparatus. Further preferably the heat treatment and the growth ofepitaxial layer are performed under a hydrogen atmosphere of ordinaryatmosphere at a temperature between 900° C. and 1080° C.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a graph showing the correlation between the number of etchpits and that of particles corresponding to that of crystal defects onepitaxial layer surface.

FIG. 2 is a map showing the distribution of the crystal defects formedon the surface of a silicon wafer. In the drawings, reference number 1denotes an inspection object for the purpose of determining crystaldefects, reference number 2 denotes crystal defects.

FIG. 3(a) is a drawing illustrating the surface condition of a siliconwafer before epitaxial growth.

FIG. 3(b) is a drawing illustrating the surface condition of a siliconwafer after epitaxial growth.

FIG. 4 is a schematic illustration of a light scattering type particleinspection apparatus.

BEST MODE FOR CARRYING OUT THE INVENTION

A preferred embodiment of the present invention will now be detailedwith reference to the accompanying drawings. It is intended, however,that unless particularly specified, dimensions, materials, relativepositions and so forth of the constituent parts in the embodiments shallbe interpreted as illustrative only not as limitative of the scope ofthe present invention.

EXAMPLE

Nine p type silicon single crystal rods having a diameter of 200 mm anda resistivity of 0.01 Ωcm ˜0.02 Ωcm were prepared, each rod having adifferent crystal defect density by varying the pulling-condition of thesingle crystal and/or the inside structure of the furnace. Then, thesilicon single crystal rods were sliced to thin plates, and the surfacesof the sliced plates were mirror polished to obtain mirror surfacewafers 310 of plane orientation of (100). (See FIGS. 3a and 3 b.) Themirror surface wafers 310 obtained from each silicon single crystal rodwere separated into two groups, one for preferential etching and anotherfor vapor phase growth.

The mirror surface wafers 310 for preferential etching were etched bysaid Secco solution, and surface defects 315 appearing as etch pits bythe preferential etching were observed by means of a Normaiski typedifferential interference microscope.

The observation by the microscope was done by scanning the main surfaceof the preferentially etched mirror surface wafers by 100× magnificationin the direction of diameter in the shape of a cross, and the number ofetch pits per wafer was calculated from the number of etch pits observedand the measurement area.

On the other hand, the mirror surface wafers 310 for vapor phase growthwere placed in a vapor phase growth furnace 300 held to a hydrogenatmosphere 320. After three minutes of heat treatment at normal pressureand a temperature of 1050° C. which results in removal of the naturaloxide film 325 while hardly etching the surface of the silicon wafer,trichlorosilane_(SiHCl₃) gas was supplied while keeping the temperatureof 1050° C. to allow an epitaxial layer 340 of 4 μm thick andresistivity of 5 Ωcm to grow at normal pressure. Thus treated waferswere prepared as inspection object silicon wafers (405 in FIG. 4). Whensaid inspection object silicon wafers 405 for the purpose of detectingcrystal defects, which are mirror surface wafers 310 with epitaxiallayer 340 formed on the surface, were measured by a light scatteringtype particle inspection apparatus 400, crystal defects such as stackingfaults₁₃(SF) and dislocation defects having pits 350 and/or projections360 were apparent on the surface of said inspection objects and detectedas particles by detecting scattered light 415 generated by light source410 with detector 420.

When said inspection object silicon wafers 405 for the purpose ofdetecting crystal defects, which are mirror surface wafers 310 withepitaxial layer 340 formed on the surface, were measured by a lightscattering type particle inspection apparatus 400, crystal defects suchas stacking faults₁₃(SF) and dislocation defects having pits 350 and/orprojections 360 were apparent on the surface of said inspection objectsand detected as particles by detecting scattered light 415 generated bylight source 410 with detector 420.

In the example, particles equal to or larger than 0.1 μm in diameterwere detected over the whole surface of the inspection object wafersexcluding the peripheral part of 5 mm from the outer edge of each wafer.

FIG. 1 shows a correlation between the number of particles on thesurface of the epitaxial layer and that of etch pits measured by thelight scattering type particle inspection apparatus in the example.

From FIG. 1, it is recognized that there is a good correlation betweenthe number of particles and that of etch pits.

FIG. 2 shows an example of measurement of crystal defects 2 appearing onthe surface of the inspection object wafer 1 manufactured according tothe aforementioned procedure.

From FIG. 2, it is recognized that the number and location of thecrystal defects formed on the surface of the mirror surface wafer areeasily determined, for the crystal defects 2 appearing on the surface ofthe epitaxial layer grown under the condition mentioned above can beoutput in a map state all over the surface of the wafer 1 throughdetection by the light scattering type particle inspection apparatuslike conventional particles have been detected.

Further, although in the example it was shown that the number andlocation of crystal defects formed on the mirror Surface wafer was ableto be detected by a light scattering type particle inspection apparatus,but also the identification of the kind of defect is possible bythinning the crystal defect part by use of a Focused Ion Beam apparatusbased on the detected information on the defects and observing the partby a transmission electron microscope.

Still further, the present invention is adaptable not only to wafershaving defects caused by crystal growth but to wafers having defectscaused by machining in the process of manufacturing mirror surfacewafers.

For example, discremination of defects caused by crystal growth fromthose caused by machining is possible in the way in which defects on thesurface of an inspection object wafer according to the present inventionare detected, then the epitaxial layer on the surface of the inspectionobject wafer is removed by mirror polishing or by non-selective etchingby use of mixed acid of hydrofluoric acid and nitric acid, etc. to get amirror surface, and after an epitaxial layer is grown again by themethod according to the present invention, defects are detected by alight scattering type particle inspection apparatus.

Although, in the example, measurement object wafers were mirror surfacewafers, silicon wafers other than the mirror surface wafers areadaptable, for example, an epitaxial wafer of which the surface is againmirror polished and which having virtually no pits and projections, asfar as pits and projections are generated by epitaxial growth.

INDUSTRIAL APPLICABILITY

As cited above, by use of the inspection object silicon wafer and methodof detection of surface defects according to the present invention, thenumber and location of the surface defects formed on the surface of thesilicon wafer can be detected.

What is claimed is:
 1. An inspection object silicon wafer for thepurpose of detecting crystal defects characterized in that epitaxialgrowth is made on a surface of a mirror surface wafer from which anatural oxide film is removed without surface defects being eliminatedto make the crystal defects having pits and projections appear on asurface of an epitaxial layer.
 2. An inspection object silicon wafer forthe purpose of detecting crystal defects manufactured through a processof heat treatment in which a natural oxide film is removed withouteliminating surface defects of a mirror surface wafer and a process ofepitaxial growth in which epitaxial growth is made on a surface of themirror surface wafer and the crystal defects are generated as defectshaving pits and projections on a surface of the epitaxial layer.
 3. Aninspection object silicon wafer for the purpose of detecting crystaldefects according to claim 2, wherein the heat treatment process andepitaxial growth process are performed under a hydrogen atmosphere ofnormal pressure at a temperature between 900° C. and 1080° C.
 4. Amethod of detecting crystal defects of a silicon wafer characterized by:making epitaxial growth on the surface of the silicon wafer heat-treatedin a temperature condition in which the natural oxide film is removedbut the surface state of the silicon wafer is preserved, wherein crystaldefects having pits and projections are made to appear on the surface ofan epitaxial layer; and detecting the crystal defects having pits andprojections by a light scattering particle inspection apparatus.
 5. Amethod of detecting crystal defects of a silicon wafer according toclaim 4, wherein the heat treatment and the growth of epitaxial layerare performed under a hydrogen atmosphere of normal pressure at atemperature between 900° C. and 1080 ° C.